From 4bfd864f10b68b71482b35c818559068ef8d5797 Mon Sep 17 00:00:00 2001 From: Thomas Voss Date: Wed, 27 Nov 2024 20:54:24 +0100 Subject: doc: Add RFC documents --- doc/rfc/rfc2171.txt | 507 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 507 insertions(+) create mode 100644 doc/rfc/rfc2171.txt (limited to 'doc/rfc/rfc2171.txt') diff --git a/doc/rfc/rfc2171.txt b/doc/rfc/rfc2171.txt new file mode 100644 index 0000000..273ffd3 --- /dev/null +++ b/doc/rfc/rfc2171.txt @@ -0,0 +1,507 @@ + + + + + + +Network Working Group K. Murakami +Request for Comments: 2171 M. Maruyama +Category: Informational NTT Laboratories + June 1997 + + MAPOS - Multiple Access Protocol over SONET/SDH Version 1 + +Status of this Memo + + This memo provides information for the Internet community. This memo + does not specify an Internet standard of any kind. Distribution of + this memo is unlimited. + +Authors' Note + + This memo documents a multiple access protocol for transmission of + network-protocol datagrams, encapsulated in High-Level Data Link + Control (HDLC) frames, over SONET/SDH. This document is NOT the + product of an IETF working group nor is it a standards track + document. It has not necessarily benefited from the widespread and + in depth community review that standards track documents receive. + +Abstract + + This document describes the protocol MAPOS, Multiple Access Protocol + over SONET/SDH, for transmitting network-protocol datagrams over + SONET/SDH. It focuses on the core protocol -- other documents listed + in the bibliography may be referenced in conjunction with this + document to provide support and services for protocols at higher + layers. + +1. Introduction + +1.1 SONET/SDH + + The Synchronous Optical Network/Synchronous Digital Hierarchy + (SONET/SDH) [1][2][3][4] family of ITU-T standard protocols are + designed to provide common, simple, and flexible interface for + broadband optical fiber transmission systems. It enables direct + octet-synchronous multiplexing of lower rate tributaries. + SONET/SDH-compliant transmission systems are widely deployed by + telephone carriers world wide. + + This document defines the MAPOS protocol -- a method for transmitting + HDLC frames over SONET/SDH. The protocol provides multiple access + capability to SONET/SDH, an inherently point-to-point link. This + enables construction of seamless networking environment using + SONET/SDH as transmission media for both LAN and WAN. + + + +Murakami & Maruyama Informational [Page 1] + +RFC 2171 MAPOS June 1997 + + +1.2 Possible Configurations + + The MAPOS protocol provides multiple access, broadcast / multicast- + capable switched LAN environment using SONET/SDH lines as + transmission media. Possible configurations of MAPOS system are + shown in the following diagrams. In (a), two end nodes are connected + to each other. Figure (b) shows a star-topology "SONET-LAN" where + multiple end nodes are connected to an HDLC frame switch. The frame + switch forwards packets between nodes and provides multiple access + capability. In (c), multiple frame switches are linked together, + creating a switching cluster. + + + +------+ +------+ + | Node +--------------------------------+ Node | + +------+ +------+ + + (a) Point-to-Point configuration + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Murakami & Maruyama Informational [Page 2] + +RFC 2171 MAPOS June 1997 + + + +------+ +---------------+ + | Node +--------------------------------+ | + +------+ | | + | | + +------+ | | + | Node +--------------------------------+ | + +------+ | | + | Frame Switch | + +------+ | | + | Node +--------------------------------+ | + +------+ | | + | | + +------+ | | + | Node +--------------------------------+ | + +------+ +---------------+ + + (b) Point-to-Multipoint configuration + + + +--------+ +--------+ + | Frame +----------------------+ Frame | + | Switch +--------+ +--------+ Switch | + +--+-----+ +-+----+-+ +--------+ + | | Frame | +--------+ + +--+-----+ | Switch | +--------+ | Frame | + | Frame | +-----+--+ | Frame +------+ Switch | + | Switch | +---------+ Switch | ++-------+ + +-------++ +--------+ | + |________________________________________| + + (c) Switching cluster configuration + + Figure 1. Possible configurations + + Each port on a switch has an unique identifier within the switch. A + node connected to a switch port must inherit the address of the port. + That is, the node address is equal to the port identifier and is + unique within the switch. + + In a switch cluster, a node address is subnetted. The high-order + bits, the part where the corresponding bits in the "subnet mask" are + 1, indicate the switch address. The remaining low-order bits + indicate the unique node address within the switch. The two fields + form an unique address for a given node. + + In either case, the address may be configured manually into a node + interface, or automatically by the address assignment mechanism + described in [5]. + + + +Murakami & Maruyama Informational [Page 3] + +RFC 2171 MAPOS June 1997 + + + Note that any two components may be connected either directly, or via + a long-haul SONET/SDH leased line. + +1.3 Packet Transmission + + The protocol is connection-less -- when a node wish to communicate + with some other node, it simply fills-in the destination address of + an HDLC frame, places it in one or more SONET/SDH payloads, and sends + it over a SONET/SDH link. + + The switch forwards the frame to its destination based on the + destination address. In a switch cluster, the frame may be forwarded + by multiple switches and is eventually delivered to the specified + node. Broadcast and multicast are also supported. Frames with an + invalid destination address are silently discarded. + + Like ethernet, the multiple access capability is provided by a switch + or a switch cluster. Since MAPOS is a link layer protocol, it is + independent of the upper layer protocols. That is, it can support any + network layer protocols such as IP. MAPOS IPv4 support is described + in [6]. + +2. Physical Layer + + This protocol treats the underlying end-to-end SONET/SDH transmission + link as if it was a plain, transparent channel. It sends HDLC frames + in SONET/SDH payloads, and expects them to arrive at the other end + unaltered. + + Each node and switch should terminate SONET/SDH overhead such as + section overhead, line overhead, and path overhead according to the + specification of SONET/SDH. Unfortunately, SONET and SDH overhead + interpretations are not identical. In addition, some SONET/SDH + implementations utilize some overhead bytes in proprietary manner. + + The detail of the interpretation is beyond the scope of this + document. Appendix A describes some of the most significant + differences among SONET, SDH, and their implementations that often + causes interoperability problems. Implementors of SONET/SDH + interfaces are strongly encouraged to be aware of such differences, + and provide workaround options in their products. + + + + + + + + + + +Murakami & Maruyama Informational [Page 4] + +RFC 2171 MAPOS June 1997 + + +3. Data Link Layer + +3.1 HDLC Frame Format + + MAPOS uses the same HDLC-like framing as used in PPP-over-SONET, + described in RFC-1662[7]. Figure 2 shows the frame format. Logical + Link Control (LLC), and Sublayer/Sub-Network Access Protocol (SNAP) + are not used. It does not include the bytes for transparency. The + fields are transmitted from left to right. + + +----------+----------+----------+----------+ + | | | | | + | Flag | Address | Control | Protocol | + | 01111110 | 8bits | 00000011 | 16 bits | + +----------+----------+----------+----------+ + +-------------+------------+----------+----------- + | | | | Inter-frame + | Information | FCS | Flag | fill or next + | | 16/32 bits | 01111110 | address + +-------------+------------+----------+------------ + + Figure 2. Frame format + + Flag Sequence + + Flag sequence is used for frame synchronization. Each frame begins + and ends with a flag sequence 01111110 (0x7E). If a frame + immediately follows another, one flag sequence may be treated as + the end of the preceding frame and the beginning of the immediately + following frame. When the line is idle, the flag sequence is to be + transmitted continuously on the line. + + Address + + The address field contains the destination HDLC address. A frame + is forwarded by a switch based on this field. It is 8 bits wide. + The LSB indicates the end of this field, and must always be 1. The + MSB is used to indicate if the frame is a unicast or a multicast + frame. The MSB of 0 means unicast, with the remaining six bits + indicating the destination node address. MSB of 1 means multicast, + with the remaining six bits indicating the group address. The + address 11111111 (0xFF) means that the frame is a broadcast frame. + The address 00000001 (0x01) is reserved to identify the control + processor inside a switch. Frames with an invalid address should + be silently discarded. + + + + + + +Murakami & Maruyama Informational [Page 5] + +RFC 2171 MAPOS June 1997 + + + +-------------+-+ + | | | | | | | | | + | | node addr |1| + +-+-----------+-+ + ^ ^ + | | + | +------- EA bit (always 1) + | + 1 : broadcast, multicast + 0 : unicast + + Figure 3 Address format + + Control + + The control field contains single octet 00000011 (0x03) which, in + HDLC nomenclature, means that the frame is an Unnumbered + Information (UI) with the Poll/Final (P/F) bit set to zero. Frames + with any other control field values should be silently discarded. + + Protocol + + The protocol field indicates the protocol to which the datagram + encapsulated in the information field belongs. It conforms to the + ISO 3309 extension mechanism, and the value for this field may be + obtained from the most recent "Assigned Numbers" [8] and "MAPOS + Version 1 Assigned Numbers" [9]. + + Information + + The information field contains the datagram for the protocol + specified in the protocol field. The length of this field may + vary, but shall not exceed 65,280 (64K - 256) octets. + + Frame Check Sequence (FCS) + + By default, the frame check sequence (FCS) field is 16-bits long. + Optionally, 32 bit FCS may be used instead. The FCS is calculated + over all bits of the address, control, protocol, and information + fields prior to escape conversions. The least significant octet of + the result is transmitted first as it contains the coefficient of + the highest term. + + Inter-frame fill + + A sending station must continuously transmit the flag sequence as + inter-frame fill after the FCS field. The inter-frame flag + sequences must be silently discarded by the receiving station. + + + +Murakami & Maruyama Informational [Page 6] + +RFC 2171 MAPOS June 1997 + + + When an under-run occurs during DMA in the sending station, it must + abort the frame transfer and continuously send the flag sequence to + indicate the error. + +3.2 Octet-Synchronous Framing + + MAPOS uses an octet stuffing procedure because it treats SONET/SDH as + a byte-oriented synchronous link. Since SONET/SDH provides + transparency, Async-Control-Character-Map (ACCM) is not used. HDLC + frames are mapped into the SONET/SDH payload as follows. + + Each HDLC frame is separated from another frame by one or more flag + sequence, 01111110 (0x7E). An escape sequence is defined to escape + the flag sequence and itself. Prior to sending the frame, but after + the FCS computation, every occurrence of 01111110 (0x7E) other than + the flags is to be converted to the sequence 01111101 01011110 (0x7D + 0x5E), and the sequence 01111101 (0x7D) is to be converted to the + sequence 01111101 01011101 (0x7D 0x5D). Upon receiving a frame, this + conversion must be reversed prior to FCS computation. + +4. Further Reading + + To fully utilize MAPOS protocol, it is useful to reference other + documents[5][6][9][10] in conjunction with this document. + +5. Security Considerations + + Security issues are not discussed in this memo. + +References + + [1] CCITT Recommendation G.707: Synchronous Digital Hierarchy Bit + Rates (1990). + + [2] CCITT Recommendation G.708: Network Node Interface for + Synchronous Digital Hierarchy (1990). + + [3] CCITT Recommendation G.709: Synchronous Multiplexing Structure + (1990). + + [4] American National Standard for Telecommunications - Digital + Hierarchy - Optical Interface Rates and Formats Specification, + ANSI T1.105-1991. + + [5] Murakami, K. and M. Maruyama, "A MAPOS version 1 Extension - + Node Switch Protocol," RFC2173, June, 1997. + + + + + +Murakami & Maruyama Informational [Page 7] + +RFC 2171 MAPOS June 1997 + + + [6] Murakami, K. and M. Maruyama, "IPv4 over MAPOS Version 1," + RFC2176, June, 1997. + + [7] Simpson, W., editor, "PPP in HDLC-like Framing," RFC1662, July + 1994. + + [8] IANA, "IANA-Assignments," + http://www.iana.org/iana/assignments.html + + [9] Maruyama, M. and K. Murakami, "MAPOS Version 1 Assigned + Numbers," RFC2172, June 1997. + + [10] Murakami, K. and M. Maruyama, "A MAPOS version 1 Extension - + Switch Switch Protocol," RFC2174, June, 1997. + +Acknowledgements + + The authors would like to acknowledge the contributions and + thoughtful suggestions of John P. Mullaney, Clark Bremer, Masayuki + Kobayashi, Paul Francis, Toshiaki Yoshida, and Takahiro Sajima. + +Author's Address + + Ken Murakami + NTT Software Laboratories + 3-9-11, Midori-cho + Musashino-shi + Tokyo-180, Japan + E-mail: murakami@ntt-20.ecl.net + + Mitsuru Maruyama + NTT Software Laboratories + 3-9-11, Midori-cho + Musashino-shi + Tokyo-180, Japan + E-mail: mitsuru@ntt-20.ecl.net + + + + + + + + + + + + + + + +Murakami & Maruyama Informational [Page 8] + +RFC 2171 MAPOS June 1997 + + +APPENDIX A. Differences among SONET, SDH, and their Implementations + + This section briefly describes the major differences among SONET + which is an ANSI standard, SDH, an ITU-T standard, and their + implementations. + + AU pointer (H1, H2, H3) + + The AU pointer consists of bytes H1, H2, and H3. The bits 5 and 6 + of the H1 byte are called "SS bits," and are used to indicate the + offset into the payload where the beginning of a SPE is located. + (Note that "SPE" is a SONET term -- SDH calls it "VC.") In the + case of OC-3c, SONET sets the SS bits of the second and the third + H1 bytes to 0, whereas SDH sets them to 10 for AU-4, and 01 for + AU-31. Although the SS bits may be ignored at the receiving + station, some transmission systems discards SONET/SDH frames with + SS bits that it doesn't expect -- the sending station should be + aware of this, and include a configuration option to handle it. + + Z1 and Z2 + + The Z bytes are reserved in SONET/SDH. Some transmission systems, + however, use them in a proprietary manner. SONET uses Z1 for Line + Error Monitoring. NTT, a carrier in Japan, utilized Z1 for + Automatic Protection Switching (APS.) + + DCC Bytes + + The D bytes are called the Data Communication channel (DCC), and + are defined for maintenance and operations. However, some carriers + and vendors use them in a proprietary manner. For example, NTT's + STM-1 UNI uses the D4, D5, and D6 bytes to transfer section and + path maintenance information. + + + + + + + + + + + + + + + + + + +Murakami & Maruyama Informational [Page 9] + -- cgit v1.2.3